Manganese‐Catalyzed Synthesis of <i>cis</i>‐β‐Amino Acid Esters through Organometallic CH Activation of Ketimines

Liu, Weiping; Zell, Daniel; John, Michael; Ackermann, Lutz

doi:10.1002/anie.201411808

Cited by 177 publications

(46 citation statements)

References 82 publications

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“…[7] First, the imines are typically limited to those prepared from less hindered aryl ketones (e.g., acetophenone,p ropiophenone,t etralone), because the imine preparation becomes less feasible with bulkier ketones.T he same limitation often applies to other N-aryl and N-alkyl-imine-directed C À Hf unctionalizations using different transition metals. [8][9][10][11][12] Second, the reaction typically stops at the monoalkylation stage,because the steric repulsion between the imine and the newly introduced alkyl group interfere with the second C À Hactivation. Forthe same reason, ortho-monosubstituted imines are reluctant to participate in the reaction.…”

Section: N à Himine As Apowerful Directing Groupfor Cobalt-catalyzed mentioning

confidence: 99%

N−H Imine as a Powerful Directing Group for Cobalt‐Catalyzed Olefin Hydroarylation

Yoshikai

2016

Angew Chem Int Ed

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N-alkyl and N-aryl imines have been frequently used as directing groups in rhodium- and cobalt-catalyzed hydroarylation reactions of olefins and alkynes. However, the scope of such hydroarylation reactions has been limited by the difficulty of preparation of sterically hindered imines by condensation, and also by the steric bulkiness of the imine group itself. Reported herein is that an N-H imine serves as an alternative and highly effective directing group for cobalt-catalyzed hydroarylation of olefins, and unlocks many of the limitations associated with the previously employed N-aryl imine directing group. The power of this minimal nitrogen directing group is manifested in a fourfold ortho alkylation of benzophenone imine, and it occurs rapidly at ambient temperature.

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Section: N à Himine As Apowerful Directing Groupfor Cobalt-catalyzed mentioning

confidence: 99%

N−H Imine as a Powerful Directing Group for Cobalt‐Catalyzed Olefin Hydroarylation

Yoshikai

2016

Angew Chem Int Ed

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“…Thep ositional selectivity of the electrochemical CÀH/NÀHf unctionalizations was dominated by steric interactions. [17] Thee lectrochemical approach was not limited to C À H/N À Ha ctivations of aromatic substrates.I ndeed, the thiophene 1q was smoothly converted likewise,w hile alkene CÀH/NÀHf unc-…”

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confidence: 99%

Electrochemical C−H/N−H Activation by Water‐Tolerant Cobalt Catalysis at Room Temperature

et al. 2018

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Electrochemistry enabled C À H/N À Hf unctionalizations at room temperature by external oxidant-free cobalt catalysis.Thus,the sustainable cobalt electrocatalysis manifold proceeds with excellent levels of chemoselectivity and positional selectivity,a nd with ample scope,t hus allowing electrochemical C À Ha ctivation under exceedingly mild reaction conditions at room temperature in water.Notably,CÀHactivation has emerged as an increasingly potent platform for molecular syntheses, [1] with transformative applications to natural product chemistry, [2] pharmaceutical industries, [3] and material sciences, [4] among others.While C À Ht ransformations have thus far largely exploited the noble transition metals palladium, iridium, ruthenium, and rhodium, recent focus has shifted towards earth-abundant, inexpensive,a nd less toxic 3d base metals. [5] Particularly, versatile cobalt catalysis has proven powerful for the functionalization of otherwise inert CÀHb onds, [6] thus enabling inter alia step-economical heterocycle syntheses by C À H/N À Hf unctionalizations. [7] Despite indisputable advances,t hese C À H/N À Halkyne annulations were as of yet strongly limited to high reaction temperatures and/or stoichiometric amounts of toxic metals as the sacrificial oxidants. [6,8] In sharp contrast, we have now unraveled the power of electrochemical [9] CÀ H [10] activation [11] to enable the first cobalt-catalyzed C À H/N À Ha lkyne annulation at ambient temperature,o nw hich we report herein. Salient features of our approach comprise 1) unprecedented electrochemical CÀH/NÀHa ctivation/ annulations,2 )isoquinolone syntheses without toxic sacrificial metal oxidants,3)fully H 2 O-tolerant electrochemical CÀ Hactivation, and 4) cobalt-catalyzed CÀHfunctionalizations, under ambient conditions,e nabled by sustainable electricity (Figure 1). In contrast to avery recent C À Hoxygenation that was restricted to the use of an access of 240 equivalents of the alcohol substrate, [12] the electrochemical CÀH/NÀHfunctionalization is operative with close to equimolar quantities in an atom-economical fashion.We initiated our studies by exploring reaction conditions for the envisioned electrochemical C À H/N À Hf unctionalization of the benzamide 1a in as imple undivided cell with ap latinum plate cathode and ar eticulated vitreous carbon (RVC) anode (Table 1a nd see Table S-1 in the Supporting Information). [13] Thus,t he desired isoquinolone 3aa was Table 1: Optimization of the electrochemical CÀH/NÀHa lkyne annulation. Entry [TM] Solvent Base Yield [%] [a] Reaction conditions: 1 (0.5 mmol), 2 (1.0 mmol), [Co] (20 mol %), base (2.0 equiv), and solvent (10 mL) at 23 8 8Cand 4mAfor 16 husing an RVC anode, Pt-plate cathode, undivided cell. [b] Oxygenation product also formed in 17 %. [c] [TM] (10 mol %). [d] 60 8 8C, 8h.[e] No electricity. acac = acetylacetonoate, DMSO = dimethylsulfoxide, Piv = pivaloyl.Figure 1. Electrochemical cobalt-catalyzed CÀH/NÀHfunctionalization at room temperature.

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“…2 Relatively few papers describe the use of abundant first-row transition metals in these reactions. 3 Among base metals, cobalt catalysis shows perhaps the highest versatility in coupling of sp 2 C–H bonds with alkenes and alkynes and in other C–H bond functionalization reactions. 4–8 An early example showing low-valent cobalt catalysis was reported by Brookhart.…”

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Cobalt-Catalyzed, Aminoquinoline-Directed Functionalization of Phosphinic Amide sp² C–H Bonds

2015

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In this paper, we introduce arylphosphinic acid aminoquinoline amides as competent substrates for cobalt-catalyzed sp2 C–H bond functionalization. Specifically, the feasibility of their coupling with alkynes, alkenes, and allyl pivalate has been demonstrated. Reactions are catalyzed by simple Co(NO3)2 hydrate in ethanol or mixed dioxane/tBuOH solvent in the presence of Mn(OAc)3·2H2O additive, sodium pivalate, or acetate base and use oxygen from the air as an oxidant. Directing group removal affords ortho-functionalized P,P-diarylphosphinic acids.

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Manganese‐Catalyzed Synthesis of cis‐β‐Amino Acid Esters through Organometallic CH Activation of Ketimines

Cited by 177 publications

References 82 publications

N−H Imine as a Powerful Directing Group for Cobalt‐Catalyzed Olefin Hydroarylation

N−H Imine as a Powerful Directing Group for Cobalt‐Catalyzed Olefin Hydroarylation

Electrochemical C−H/N−H Activation by Water‐Tolerant Cobalt Catalysis at Room Temperature

Cobalt-Catalyzed, Aminoquinoline-Directed Functionalization of Phosphinic Amide sp² C–H Bonds

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Manganese‐Catalyzed Synthesis of cis‐β‐Amino Acid Esters through Organometallic CH Activation of Ketimines

Cited by 177 publications

References 82 publications

N−H Imine as a Powerful Directing Group for Cobalt‐Catalyzed Olefin Hydroarylation

N−H Imine as a Powerful Directing Group for Cobalt‐Catalyzed Olefin Hydroarylation

Electrochemical C−H/N−H Activation by Water‐Tolerant Cobalt Catalysis at Room Temperature

Cobalt-Catalyzed, Aminoquinoline-Directed Functionalization of Phosphinic Amide sp2 C–H Bonds

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Cobalt-Catalyzed, Aminoquinoline-Directed Functionalization of Phosphinic Amide sp² C–H Bonds